Characterization of posttranslational protein modifications isolated from Milk and dark chocolate.

Chocolate represents a highly processed food due to fermentation, roasting and conching during manufacturing. However, up to now there are only a few and contradictory data published for the formation of advanced glycation endproducts (AGEs). With the present report a novel quantitative method for the characterization of the whole protein fraction from chocolate was developed and 9 Maillard reaction products and 3 other posttranslational modifications in addition to furosine were determined by HPLC-MS/MS. Cocoa proteins were found to be much higher modified compared to caseins as present in milk chocolate (e.g. N6-carboxyethyl lysine 322 mg/kg vs. 57 mg/kg protein). Unexpectedly, N6-formyl lysine was found as a major AGE reaching up to 1251 mg/kg protein. Milk chocolate contained in total 17.3 mg/100 g AGEs while dark chocolate had 33.5 mg/100 g in average. According to this, chocolate was identified as an important source for AGE uptake within the human diet.